1. Field of the Invention
This invention relates generally to landscape and agricultural irrigation and more particularly concerns a machine executed method and system for irrigation control and management using weather data and water usage restrictions which results in a high level of usage efficiency and water conservation.
2. Description of the Related Art
Many attempts have been made in the past to provide reliable systems for maintaining an optimum amount of water in the soil for growing crops such as lawns, flowers, gardens and farm produce. Automatic systems are well-known which operate on a predetermined time sequence which may be adjusted for seasonal and atmospheric conditions. However, prior art irrigation systems have not generally combined weather data with water budget data to allow an operator to determine an optimum amount of water to apply at an irrigation station based on plant water replacement needs and water budget restrictions. Those systems which have employed some rudimentary form of budget control wherein central management personnel at a distantly remote central computer controls the amount of water allocated for a plurality of stations have an inherent disadvantage due to their inability to view the actual plant material. The viewing of the plant material gives a valuable feedback to the individual who makes the decision about how much water is to be applied but this visual feedback needs to be tempered with a budget requirement. Some prior art systems allow a plant viewing groundskeeper to call central management and request water to be applied at a certain location, but this is cumbersome and presents problems because of conflicts of interest between a manager who is concerned primarily with the cost of water and the groundskeeper who is concerned with plant appearance. Typically, a groundskeeper's or an operator's task has been to keep landscaping material looking healthy (e.g., keeping the grass green) but there is no balancing motivation to conserve water. Thus, the operator has no incentive to maintain a irrigation system at high operating efficiency and in good repair to limit and therefore conserve water. Unfortunately, even the best sensing and data collecting systems can be overcome by an operator who is motivated solely by the appearance of the plant. A further disadvantage of prior art systems that do not have a water budget allowance is that there is no motivation for the operator to be creative, for example, by selecting plant material that requires less water. It can be seen that a lack of cooperative control between central management and groundskeepers who can actually view the plants leads to unsatisfactory results.
An interactive irrigation control system is disclosed in U.S. Pat. No. 4,176,395 to Evelyn-Veere. The Evelyn-Veere patent concerns an irrigation control system and a related method for controlling valves in accordance with schedules of instructions. A general control system, such as the Evelyn-Veere invention, relies on the traditional method of sensing moisture in the soil for controlling the irrigation. A drawback of systems that utilize moisture sensing probes inserted into the soil is that they are usually insufficiently sensitive, especially at high moisture saturation levels. Still another problem with prior art systems that rely on moisture sensing probes in the soil is that it is exceptionally difficult to train poorly educated operators to have the skills needed for proper operation. Unfortunately, the Evelyn-Veere patent discloses no method or system for collecting and maintaining weather data at a station to be irrigated such that an irrigation station's water demands can be established from such data. Nor does the patent disclose the use of water budget restrictions combined with such weather data in order to conserve water while preserving the health of the plants.
Prior art systems have another drawback in that no corrective factor is made to account for the evapotranspiration characteristics of the plant material being grown or the efficiency of the water application device (e.g. a sprinkler or the irrigation system). Evapotranspiration (ET) refers to the amount of water a plant loses and needs to have replaced in order for the plant to maintain optimal growth. A reference value, ET.sub.0, has been established for a particular type of plant--pasture-type tall fescue mowed to 4 to 6 inches in height and maintained in optimal condition. For example, if the ET.sub.0 value is 0.20 inches, then pasture-type tall fescue mowed to 4-6 inches in height would need 0.20 inches of water for that day in order to maintain optimal growth. Other plants' water needs can be referenced as a percentage of ET.sub.0 or % ET.sub.0. Typically, most plants used for landscaping purposes require less water than tall fescue. This % ET.sub.0 value is often called a crop coefficient factor or multiplier. For example, Bermuda grass uses about 60% of the water that the reference plant needs so its % ET.sub.0 value is 60. Assuming that the ET.sub.0 value for that day is 0.20 inches, then the Bermuda grass water needs are calculated as 60 percent of 0.20, or 0.12 inches. Since ET rates are different according to the type of plant, the rate of water lost is dependent on the type of plant. Prior art systems which rely on sensing soil moisture without accounting for the ET of a particular plant are not as accurate in determining the optimum amount of water to be replaced. Prior art systems that do not account for the efficiency of the irrigation system when determining how much water to apply by an irrigation station typically lead to inaccurate assessments of how much water is actually needed by or delivered to the plants or crops.
In the interest of completing the background of this invention, reference may be made to the following article, Hodel, "Quantify Accurate Irrigation Schedules with ET Data," California Landscaping, February 1994. This article explains how to use ET.sub.0 data to determine irrigation water replacement needs. The article does not disclose an automatic system and method that combines weather data with water budget information to determine an optimum amount of water to apply.